Seems to me an iPhone 4S will be an iPhone 4S, no matter who the carrier is. I'm guessing Sprint and Verizon may try to lock them so that you can't port them for activation between the two carriers. Then again maybe not. If you buy it from Apple, you should be able to use it on any carrier you chose. If they do lock them through software, no doubt someone will figure how to unlock them fairly easily. Anyway, here's the info. on connectivity from CNET:

Connectivity As widely reported, the iPhone 4S is a dual-band world phone, meaning it supports both GSM and CDMA. This is more significant for Verizon and Sprint customers, as it will allow them to use the iPhone even if they travel overseas. What's yet to be determined is whether the carriers will unlock the preloaded SIM card, so users can swap it out for a prepaid international SIM card at their destination. We also don't know if the CDMA models will offer simultaneous voice and data over the CDMA network. At present, that's a significant limitation of the Verizon iPhone 4.

Meanwhile, for GSM customers, the iPhone 4S now supports HSPA+ 14.4, so the smartphone is capable of reaching theoretical download speeds of 14.4Mbps down, 5.8Mbps up. It's certainly an improvement over the current model, but disappointing that there's no compatibility with the faster HSPA+ 21Mbps networks.

Of course, the lack of "real" 4G support for LTE on Verizon or WiMax on Sprint is troubling. Apple has its reasons, no doubt. Battery life remains an issue for high-speed phones and Apple must have decided that, at this point, it couldn't offer its optimal customer experience on a 4G handset (remember that customer experience is really what Apple is all about). Secondly, Apple never jumps on a technology that is still growing, and it must think that 4G doesn't cover enough people quite yet.

Switching out the sims may allow international use, but getting a Verizon iPhone to activate on Sprint will not work by any means. It's the same reason the current Verizon or CDMA phones cannot be activated on Sprint's post-paid CDMA. We have a very specific MEID data base and if it's not loaded, it WILL NOT ACTIVATE. Even Boost Mobile CDMA phones will not activate on the post-paid CDMA Sprint network.

Switching out the sims may allow international use, but getting a Verizon iPhone to activate on Sprint will not work by any means. It's the same reason the current Verizon or CDMA phones cannot be activated on Sprint's post-paid CDMA. We have a very specific MEID data base and if it's not loaded, it WILL NOT ACTIVATE. Even Boost Mobile CDMA phones will not activate on the post-paid CDMA Sprint network.